After nine episodes of serving up a mixture of highs and lows over the series so far, Star Trek: Discovery reaches its midseason finale point with plenty of action and a lot of heart.

In 'Into the Forest I Go', Discovery hits that familiar series snag of trying to juggle its two major storylines in one engaging episode, jumping between its spore-drive narrative and its Klingon war story – but not necessarily with ease.

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However, what the series does have this week is Captain Lorca (Jason Isaacs) bridging the gap between both arcs while Lt Stamets (Anthony Rapp) steps up to play a key role in the war effort, and the episode is all the better for it.

For most of Discovery so far, Stamets has served as the Discovery's means to a quick getaway and his health has suffered for it, but here Lorca taps into that ruthless, warmongering part of himself and talks Stamets into putting his life in even more danger by agreeing to perform 133 consecutive micro-jumps – despite knowing that the spore technology is literally changing Stamets' brain matter.

It's a move that is pure Lorca: manipulating Stamets into agreeing with Lorca's own desire to be a war hero by appealing to Stamets' own interests of science and exploration. In doing more jumps, Lorca posits, Stamets will be better able to explore the secrets of the universe in the field, rather than in a lab like most scientists.

But first, he has to make these 133 jumps around the Klingon Ship of the Dead to provide data for an algorithm that will help the crew de-cloak the Klingon's cloaked ships and destroy them. Or, to put it in their own words: Stamets has to do this so they can win the war, and then the journey can continue.

In order to do this, the Discovery must send a boarding party to the Klingon ship and set up sensors that will help the Discovery collect all the data it needs, which is a task that falls to the ship's new go-to sub-team, Tyler (Shazad Latif) and Burnham (Sonequa Martin-Green), much to Lorca's disapproval.

It does feel odd that a Captain who convinced his Chief Engineer to risk his life for the war effort would hesitate at sending a convicted mutineer on a mission to do the same thing. Whatever the writers may have in store for this particular pairing later on in the series, there just isn't enough of it in the show already for this entire exchange to make a whole lot of sense.

Unless, of course, it was all part of a muddled plan to give Burnham the chance to plead her case, which she does so successfully thanks to a brilliant turn (as ever) from Martin-Green. Not only is she the most qualified crew member to place the sensors, Burnham argues, but she's also the most expendable, only part of the crew on borrowed time and purely here to help them win the war.

It's hard to argue with those kind of facts, so Burnham and Tyler are beamed on board the Klingon ship as Kol wages war on Starfleet's "enchanted" Discovery. And, however long it may have taken to set up this scenario, there's no denying it was definitely worth the wait.

The mission is risky and suspenseful (even if it did seem a little too easy for two humans to walk around an armed enemy war vessel undetected, tech or no tech) and culminated in one of the best action sequences the show has given us yet.

With the sensors in place and the Discovery jumping around the Klingon vessel, Burnham faces down Kol (Kenneth Mitchell) and challenges him to combat in a bid to keep the Klingons distracted from escaping the trap that Discovery is setting.

For Tyler, on the other hand, the mission to the Klingon ship forces him to confront some painful memories when he comes face-to face with his captor and his torturer L'Rell (Mary Chieffo) once again and has severe PTSD flashbacks of his time in prison.

Wherever you stand on that fan theory, Shazad Latif performed brilliantly here as a man trying to live with a traumatic event in his past – and the fact that L'Rell has come along for the next stage of the Discovery ride gives the show plenty of time to give this story a lot more attention in episodes to come.

No, with the episode's end, the Discovery is well and truly lost in space when Stamets' "one final jump" to bring the Discovery home predictably goes wrong, leaving the Discovery in unknown territory and their means of navigation blind and incoherent.

There's a lot to like about 'Into the Forest I Go', intense action and strong character beats among them. The love and commitment between Stamets and Dr Culber (Wilson Cruz) is shown more effectively this week in Culber's concern and one quick kiss than it has been all season long, while Burnham and Tyler's respect and affection for each other has grown very naturally, leading to a very touching interaction between the pair.

However, the end of the episode proves that Discovery as a series still seems to be finding its feet. With the main bulk of the action over, the episode falters and stumbles around loose ends and new ideas until it walks into a conclusion that seemingly launches another soft reboot akin to the shake-up we saw in episode three.

That's not to say it doesn't leave the audience with a lot of questions left to ponder over its near two-month break – it does, and it's clear there are still plenty of mysteries to uncover here.

But if this first block of episodes have told us anything, it's that the characters are holding down the bridge while the story warps in and out around them when it suits, which is something that needs to be fixed quickly when the series returns.

Star Trek: Discovery returns to CBS All Access in the US on January 7, 2018. Netflix airs the show in the UK.